Audion tube



W. J. ALBERSHEIM AUDION TUBE Nov. 26, 1929.

Filed may 18. 1926 75 avwantoz wcxcu I. Olkusk m 951 K flame t,

Patented Nov. 26, 1929 UNITED STATES TEN WALTER J. ALBERSHEIM, OF NEWYORK, N. Y., ASSIGNOR TO RADIO CORPORATION OF AMERICA, OF NEW YORK, N.Y.,

A CORPORATION OF DELAWARE AUDION TUBE Application filed May 18 Thisinvention relates more particularly to a class of devices for detectingand amplifyin wireless electric signals.

y invention has for its object primarily to provide an audion tubedesigned to be employed in wireless electric or so-called radio systemsfor improving the quality of transmission, detection and amplificationof the signal waves by diminishing the tendency to regeneration or feedback by capacitive conductance of the signals through the medium of astabilizer provided within the tube for modifyingv the electrostaticfield surrounding the steering or current input electrode of the device.The stabilizer having a fixed potential serves the purpose of overcomingoscillations which tend to cause whistling and noisy howls in thesignals passing through the tube.

The invention resides mainly in the provision of conductive means in theform of an independent electrode or grid which leads from the cathode orfilament or thermionic means into the space through which flows thestream of electrons from the cathode to the anode through the usualinput electrode of the device. The independent electrode is free of allcircuit connections exteriorly of the tube other than its connections tothe filament for serving to stabilize the electrostatic fieldsurrounding the input electrode by diminishing the influence offluctuations of the cathode or anode voltage on the input electrode.

A further object of the invention is to provide an audion tube of asimple and efficient construction which may be made in appropriate sizesand shapes.

With these and other objects in view, the invention will be hereinaftermore fully described with reference to the accompanying drawleg forminga part of this specification in which similar characters of referenceindicate corresponding'parts in all the views, and will then be pointedout in the claims at the effd of the description.-

In the drawing, Figure 1 is a diagrammatio view of an arrangement ofcircuits employing one form of audion tube embodying my invention.

. 1926. Serial No. 109,927.

Fig. 2 is a sectional view, partly in elevation, taken through thedevice.

Fig. 3 is a plan view taken on the line 33 of Fig. 2.

Fig. 4 is a diagrammatic view of an .arrangement of circuits employing aslightly modified form of the device.

Fig. 5 is a sectional view, partly in elevation, taken through themodified form of the device, and

Fig. 6 is a plan view taken on the line 66 of Fig. 5.

The form of the device shown in'Figs. 1, 2, 3 has the evacuated bulb orenvelope 10 with its lower part sealed in an insulated base 11.Extending upwardly interiorly of the bulb from the base 11 is asupporting stem, as 12, of glass or other insulating material, and allof these parts may be of appropriate sizes and shapes.

Projecting from the supporting stem 12 upwardly towards the top of thebulb 10 is a nonconductive rod or member 13 which may be of the shape ofan inverted L toprovide an arm 14 extending toward and terminating on avertical line corresponding to the central part of the supporting stem.Protruding from the underside of the base 11 are two spaced conductiveposts 15, 16, and leading from these posts through the base and throughthe supporting stem 12 are two conductors or wires 17, 18 which lead tothe cathode or filament 19 which is of somewhat the shape of an invertedU. The central or neutral part, as 19", of the spanning member of theU-shaped filament is supported on the free end portion of the arm 14 ofthe nonconductive L-shaped rod 13. Surrounding the filament 19 is anannular or sleeve like metallic plate element or output anode 20-of sucha diameter that it is spaced some distance from the filament, and theanode is approximately of a similar length to the length of the filament. Part of the anode 20 is supported on the upper portion of a rod,as 21, having its other end embedded, at 22, in the insulated supportingstem 12, and the opposite part of the annular anode is supported on theupper part of a metallic rod or conductor 23'which leads through thesupporting stem 12 and through the base 11 to the conductive post 24which protrudes from the underside of the base in spaced relation to theposts 15, 16. When heated the cathode or filament 19 serves asthermionic means for producing a. stream of electrons to the anode 20,as will be later explained.

Surrounding the filament 19 is an annular input electrode or steeringgrid 25 which is preferably composed of metal wire wrapped helically onthe upper portions of two spaced metallic rods or conductors 26, 27 sothat the convolutions of the grid are spaced from each other. The lowerend of the conductor 26 is embedded, at 28, in the insulated supportingstem 12, and the conductor 27 leads through the supporting stem 12 andthrough the base 11 to a conductive post 29 which extends from theunderside of the base 11 in spaced relation to the posts 15, 16 of thefilament 19 and to the post 24 of the anode or plate 20. The annulargrid 25 is of nearly the same length as the length of the anode 20, andthe grid is of such a circumference that it is spaced closer to theanode than to the filament or thermionic means 19. The grid 25 istherefore in the space or path for the stream of electrons to passtherethrough from the filament to the anode.

Between the filament 19 and the steering rid 25 is a stabilizer 30preferably in the orm of an annular electrode or grid for serving tomodify the electrostatic field sur rounding the input electrode or grid25. The stabilizing electrode 30 is also preferably composed of metalwire wrapped spirally on the upper portions of two spaced metallic rodsor conductors 31, 32 so that the convolutions of the winding are inspaced relation, and one end, as 36, of the stabilizing elect-rode leadsto the neutral part 19 of the filament. The lower ends of both of theconductors 31, 32 are embedded, at 33, 34, respectively, in theinsulated supporting stem 12. The conductors 31, 32 do not lead directlyto the exterior of the tube, and have no circuit connections other thanthrough the filament. The device is therefore of the usual form havingthe four conductive posts 15, 16, 24, 29.

In practice this form of the device may be used in an amplifying orradio circuit, as 35, Fig. 1. In the circuit is the battery A or othersource of direct or alternating current supply for heating the filament19, and the battery and filament are connected by a conductor 37 toanother battery B or other source of direct current supply. The inputcircuit includes the antenna 39 which receives the high frequency wavesignals for flowing through the primary coil 40 of an input transformer41 to ground, as 42. One end of the secondary coil 43 of thetransforme'r 41 leads by a conductor 44 to the steering grid 25, and theother end of the secondary coil leads by a conductor 45 to apotentiometer 46. The potentiometer 46 is connected to the ends of thefilament 19 by a conductor 47 and a conductor 48. Leading from thesecondary coil 43 to the conductor 44 is a conductor 49 in which isinterposed a variable condenser 50. With the heating of the cathode orfilament 19 by the battery A the current is shunted to the potentiometer46 over conductors 47, 48. The potential of the grid 25 is madesubstantially equal to that of the filament by the conductive connection45 to the potentiometer, and the secondary coil 43 of the transformer 41is tuned by the variable condenser 50. The voltage alternations ofthecurrent through the conductor 44 from the secondary coil are imposedon the electrode or grid 25 which vary its potential relative to thefilament potential. The oscillations of the grid potential will therebyvary the intensity of the space current or stream of electrons flowingfrom the filament 19 to the anode or plate 20 through the stabilizingelectrode 30. The output or plate circuit includes the conductor 51which leads to one end of the primary in ductance or coil 52 of theoutput transformer 53, and the coil 52 leads by a conductor 54 to thebattery B. From this battery the current will flow over conductor 37 tothe filament 19. The alternations of the space current in the coil 53will induce an alternating voltage in the secondary coil 55 of thetransformer 53 which may be detected in this unit or further amplifiedas desired. If the current from the battery A produces an alternating orfluctuating voltage in-the filament 19 these fluctuations will vary thesteering electrostatic potential between the filament and the grid 25 ina similar Way as the fluctuations from the grid itself. They willtherefore be amplified in the bulb and cause undesirable fluctuations ofthe output voltage. These undesirable fluctuations are diminished by thestabilizing electrode or grid 30, which grid has a shape similar to thesteering grid 25, and 1s interposed between the stabilizing electrode 30and the filament. The electrode 30 being conductively connected, at 36,to the neutral point 19 of the filament has a fixed potential, and beinginterposed in the stream of electrons between the filament and grid 25serves to diminish the influence of the fluctuations of the filamentvoltage on the steering grid, and in turn effects a quieter'operation ofthe amplifying system.

The form of the device 55' illustrated 1n Figs. 4, 5, 6 has theevacuated bulb 56, base 57, insulated sup orting stem 58, U-shapedfilament or catho e 59 with its conductors 60,

- 61 leading to the posts 62, 63 which protrudes element or output anode64 which is of such a circumference that it surrounds and is spaced fromthe filament 59. Part of this anode is supported on the upper portion ofa rod 65 having its lower end embedded, at 66, in the insulated stem 58,and the opposite part of the anode is supported on the upper part of ametal rod or conductor 67 which leads through the supporting stem 58,and through the base 57 to a conductive post 68 extending from theunderside of the base in spaced relation to the posts 62, 63.Surrounding the filament 59 is an annular steering electrode or inputgrid 69 which is formed of metal wire wrapped spirally on the upperportions of two spaced rods or conductors 70, 71 so that theconvolutions of the winding are spaced from each other, and thissteering grid is of such a circumference that it is spaced from thefilament. The anode 64 and the grid 69 are of lengths approximatelysimilar to the length of the filament 59 proper. The lower end of therod 70 of the steering grid 69 is embedded, at 72, in the supportingstem 58, and the conductor 71 leads through this supporting stem andthrough the base 57 to a post 73 Which protrudes from the underside ofthe base in spaced relation to the posts 62, 63, 68.

Between steering grid 69 and the anode 64 is a stabilizer for modifyingthe electrostatic field or capacitive conductance between the filament59 and anode 64. The stabilizer 74 is preferably in the form of anelectrode or grid composed of metal Wire wrapped spirally on the upperportions of two spaced rods 75, 76 having their lower ends embeddedrespectively, at 77, 78, in the insulated stem 58. The convolutions ofthe winding of the stabilizing electrode 74 are spaced from each other,and this electrode is of sufficient diameter and is positioned so thatit surrounds the steering grid 69 about midway between the anode 64 andthe steering grid 69. The stabilizing electrode 74 is therefore in thespace or path for the flow of the stream of electrons from the filament59 to the anode 64, and the upper end, as 79, of the winding of theelectrode 74 leads to the neutral point, as 80, of the spanning memberof the U-shaped filament 59, this part of the filament being suspendedon the end of an arm 81 of an inverted L-shaped rod 82 having the lowerend of its other arm embedded, at 83, in the supporting stem member 58.The stabilizing electrode 74 as provided has no conductive connectionexteriorly of the tube other than its connection 79 to the filament 59.

This form of the device 55' is adapted to be employed in a highfrequency amplifying or radio circuit 84, Fig. 4. When the device isarranged in the circuit the filament 59 is heated from the current ofthe battery C or other source of direct or alternating current supply,and a conductor 85 also leads to this filament and to the battery C froma second batery D or other source of direct current supply. The input ofthe circuit 84 includes the antenna 86 which receives the high frequencywave signals which pass through the primary coil 87 of an inputtransformer 88 to ground, as 89. One end of the secondary coil 90 of thetransformer 88 leads bya conductor 91 to the input or steering grid69,,and the other end of the secondary coil leads by a conductor 92 tothe filament 59. A resistance or rheostat 93 is interposed in thefilament heating circuit by a conductor 94 which leads from the batteryC and by a conductor 95 which leads from the resistance 93 to theconductor 92. Leading from the secondary coil 90 to the conductor 91 isa conductor 96 in which is interposed a variable condenser 97. Thecurrent heating the cathode or filament 59 from the battery C isregulated by the resistance 93 over conductors 85, 94, 95. The potentialof the tuned input inductance of the secondary coil 90 of the inputtransformer 88 is made equal to that of the filament by the connection92 to the conductor 95, and the high frequenc voltage in the secondarycoil 90 of the transformer 88 is amplified by the variable condenser 97in the circuit over conductor 96. The voltage alternations of thecurrent through the conductor 91 from the secondary coil 90 are imposedon the electrode or grid 69 which vary its potential relative to thefilament potential. The oscillations of the grid potential will thenvary the intensity of the space current or stream of electrons flowingfrom the filament 59 to the anode or plate 64 through the grid 69 andthrough the stabilizing electrode 74. The output or plate circuitincludes the conductor 98 which leads to one end of the primaryinductance or coil 99 of the output transformer 100, and this coil 99leads b a-conductor 101 to the battery D. From t e batery D the currentwill pass over conductor 85 to the filament. The alternations in thespace current in the coil 99 will induce an alternating voltage in thesecondary coil 102 of the transformer which may be further amplified inthe same way as the secondary voltage of the input transformer 88 bymeans of a tuning condenser 103. It is known that the electrostaticfield between the anode 64 and the grid 69 forms a capacitive connectionbetween the output circuit and input circuit with resultant detrimentaleflect; first, the fluctuations of the plate voltage caused by the spacecurrent fluctuations in the output circuit tend to counteract thegoverning effect of the steering grid and limit the amplifying ratio ofthe audion device; second, if the output and input circuit are tuned tothe same frequency, the capacitive connection may feed back sufficientenergy from the output circu t to the input circuit to causeregeneration which will make the circuit unstable and produce whistlingand howling noises. These defects are met by means of the stabilizingelectrode 74 which being connected to the filament 59 by its portion 7 9is interposed between the steering grid 69 and the anode 64. Thestabilizing electrode thereby serves to weaken the undesiredelectrostatic field or capacitive conductance between the grid 69 andthe anode 64 for increasing the amplifying ratio of the tube anddiminishing the feed back effect to avoid oscillations, howls andwhistling.

In the foregoing description, I have embodied the prcferred form of myinvention, but I do not wish to be understood as limiting myselfthereto, as I am aware that modifications may be made therein withoutdeparting from the principle or sacrificing any of the advantages ofthis invention, therefore, I reserve to myself the ri ht to make suchchanges as fairly fall within the scope thereof.

Having thus described my invention, I claim as new and desire to secureby Letters Patent 1. An audion tube comprising an anode, a filamentarycathode, a perforated input electrode, and a second perforated electrodeelectrically connected to the center of said cathode within said tube,-said second electrode being positioned between the cathode and theanode.

2. An audion tube comprising an anode, an

input grid, an electron emitting cathode, and

a second electrode positioned between the input grid and the anode, saidsecond electrode being electrically connected to the center of thecathode within said tube.

This specification signed and witnessed this 17th day of May A. D. 1926.

WALTER J. ALBERSHEIM.

